Acute kidney injury remains a global challenge, and despite the availability of dialysis and transplantation, can be fatal. Individuals who survive an acute kidney injury are at increased risk of developing chronic kidney disease and end-stage renal failure. Acute injury of the kidney may occur from sterile inflammation associated with lack of blood flow and oxygenation termed ischemia, and from ascending urinary tract infections termed pyelonephritis.cUnderstanding the fundamental mechanisms underpinning the pathophysiology of acute kidney injury is critical for future development of novel strategies for diagnosis and treatment. A growing body of evidence indicates that amplifying type II immunity may have therapeutic potential in sterile kidney injury and disease. Of particular interest are a recently described subset of innate lymphocytes called group 2 innate lymphoid cells. Group 2 innate lymphoid cells are crucial tissue-resident immune cells that maintain homeostasis and regulate tissue repair at multiple organ sites, including the kidney. They are also critical mediators of type 2 immune responses following infection and injury. The existing literature suggests that activation of group 2 innate lymphoid cells and production of a local type 2 immune milieu is protective against sterile kidney injury and the associated pathology. Several studies used a gain-of-function approach whereby administration of alarmins such as interleukin-33 prior to and/or after injury. Yet, it is unknown whether the specific depletion of the group 2 innate lymphoid cells would impair the ability of the kidney to repair or whether the injury would be exaggerated if a loss-of-function approach were used. However, in the context of non-sterile kidney injury far less is known about type II immune pathways. Whilst the interleukin-33 is increased in the urinary bladder following infection in pre-clinical models, the effect of exogenous interleukin-33 is yet to be explored in this context. Before considering interleukin-33 or other type II immunotherapies for sterile kidney injury, it is essential to explore the role of these factors in a non-sterile context due to the global prevalence of urinary tract infections. In Chapter 3 of this thesis, I characterised the phenotype of group 2 innate lymphoid cells in the kidney and contrasted them against the same cells in the lung in terms of cell surface antigen expression and key type II cytokines, interleukin-5 and interleukin-13. Next, I demonstrated that these cells can be identified in cleared tissue sections using cytokine reporter mice and determined that these cells are primarily localised around the vasculature of the mouse kidney. Finally, I performed specific loss-of-function studies using a range of genetically modified mice, which were constitutively deficient in group 2 innate lymphoid cells, and others which were conditionally depleted of these cells by administration of the diphtheria toxoid; and found that reduction of these cells does not impact on the severity of sterile kidney injury induced by surgical blood flow restriction and ischemia. In Chapter 4, I confirmed reports from others and found that the interleukin-33 was increased during uropathogenic Escherichia coli infection in the urinary bladder and kidney, respectively. Next, I demonstrated that administration of the recombinant mouse interleukin-33 prior to infection was sufficient to exaggerate the proportion of animals with kidney infection, termed pyelonephritis. Yet interestingly, it did not alter the kinetics of bladder infection, termed cystitis. Additionally, I discovered that Escherichia coli-induced pyelonephritis caused a noteworthy kidney injury, as seen in tissue histopathology; and kidney function was impaired, as measured by transcutaneous glomerular filtration rate. Similar to the kidney, I found that group 2 innate lymphoid cells in the bladder can be identified using interleukin-5 reporter systems. Yet there were some inherent differences in the cell surface markers between these two tissues as determined by unsupervised clustering from flow cytometry. Whilst group 2 innate lymphoid cells were found in the urinary bladder and were localised around the vasculature, specific depletion of these cells by diphtheria toxoid did not induce any obvious phenotype during infection. Finally, I observed that the interleukin-22 levels were decreased following infection with exogenous interleukin-33 pre-treatment. In Chapter 5, I found that the interleukin-22 protein was largely undetectable in the urinary bladder under homeostatic conditions, was highly variable in the kidney, and that the levels were unchanged by circadian rhythm or sex. However, low interleukin-22 low levels were correlated with worse infection in the kidney. Next, I demonstrated that the urinary bladder and kidney express the membranous receptor to respond to interleukin-22, and found that systemic administration of the recombinant cytokine was sufficient to activate downstream pathways in the kidney only. Finally, I demonstrated that exogenous interleukin-22 was protective against pyelonephritis in almost all cases when administered 12 hours after infection, yet the pre-treatment regime was ineffective. Within this thesis, several knowledge gaps around our understanding of type II immunity and the function of group 2 innate lymphoid cells was investigated in the urinary bladder and kidney. I demonstrated the phenotype of group 2 innate lymphoid cells was unique between the urinary bladder and kidney under homeostatic conditions. I also determined that interleukin-5 reporter systems were able to be used to pinpoint the location of these cells in both tissues, and that the group 2 innate lymphoid cells are localised around the vasculature. Using a combination of loss- and gain-of-function approaches the function of these cells was explored with sterile kidney injury, and urinary tract infection models. Overall, I find that depletion of these cells using diphtheria toxoid cause no significant changes in kidney injury, yet exogenous interleukin-33 caused a phenotype of exaggerated kidney infection with concurrent low interleukin-22 levels. Finally, I discovered that exogenous interleukin-22 was sufficient to protect against kidney infection.
Copyright © 2021 Guy John-Malcolm Cameron